/Engine/Plugins/Media/ElectraCodecs/Source/ElectraDecoders/Public/IElectraDecoderOutputAudio.h
Returns the number of frames one input access unit will decode into. This could be different than what is known by the container format. For instance, a HE-AAC stream may decode into twice the sampling rate and thus twice the number of decoded frames if the decoder supports it.
int32 GetNumFrames() const